Ambulocetus: Early Whale

Ambulocetus is a famous "missing-link" animal that lived during the Eocene Epoch of the Cenozoic. It has been suggested that this mammals formed the bridge between terrestrial mammals and marine whales, which if true would mean that whales are direct descendants from animals that moved around on land. Fossils of ambulocetus have been found primarily in Pakistan.

Ambulocetus was about the size of a sea lion and weighed an estimated 650 pounds. It had a small hoof at the end of each toe, which was shared by other early terrestrial mammals of the Eocene, but also had a number of very different characteristics. It had very whale-like skull characteristics such as an elongated snout and large sigmoid process (a crest on the tympanic bone). It had short, powerful legs that would have helped it to move about on land and also a long tail which probably aided it in swimming in the water. It is likely that it swam by using an undulating motion due to its lack of developed flippers to propel it forward. This style of movement is shared by certain marine mammals like otters today. There is an absence of a tail fluke as well, so ambulocetus would have need to move its body in a kind of armless butterfly stroke, with its limbs held close to its body to reduce drag in the water.

Ambulocetus probably hunted on land as well as on water. Because its back legs were unsuitable for land, it is unlikely that the animal could have moved very fast across the ground after prey. Thus, it was likely it was an ambush predator on land, using stealth and camouflage in order to allow prey close enough to its jaws. In water it was probably much more swift and mobile, able to either chase down fish or ambush prey on the shore by using a method of attack similar to that of modern crocodiles. Hovering near the surface of the water it would wait until a prey item would get close to the water to drink, then use a powerful stroke to thrust it forward out of the water and latch onto the prey with its jaws. Also like a crocodile, it would hold the prey in its viselike jaws and long teeth long enough for it to drown. Ambulocetus lacked ears, so it would not be able to hear on land as other mammals did. However, like a whale, it probably could have picked up vibrations in the water or on the ground by using its jaw as a hearing organ.

Ambulocetus paved the way for a new golden age of large marine animals. Except this time it would not be reptiles or fish that held supremacy over the seas, but mammals.